A frequent complaint of users of hearing devices, especially when they start wearing them for the first time, is that the sound of their own voice is too loud or that it sounds like they are talking into a barrel. Both effects are particularly pronounced when the ear canal (commonly also referred to as the auditory canal) is sealed, e.g. by an otoplastic. Accordingly, there exists the need to identify the presence or activity of the own voice of the user of a hearing device to be able to process the user's own voice in a different way than sound originating from other sources.
Methods for own-voice detection are commonly based on quantities that can be derived from a single microphone signal measured at an ear of a user, such as for example overall level, pitch, spectral shape, spectral comparison of auto-correlation and auto-correlation of predictor coefficients, cepstral coefficients, prosodic features, or modulation metrics. However, the degree of achieving reliable own-voice detection is rather poor when using methods based on such measures.
EP 1 956 589 A1 discloses a method for identifying the user's own voice by assessing a direct-to-reverberant ratio between the signal energy of a direct sound part and that of a reverberant sound part of at least a portion of a recorded sound. It is stated that this allows a very reliable own-voice detection. However, to achieve this a rather complex signal analysis is required.
WO 2004/077090 discloses a method for detection of own voice activity in a communication system which seeks to improve detection reliability. Hereto, own-voice detection is based on a combination of a number of individual detectors, each of which may be error-prone, whereas the combined detector is asserted to be robust. A signal processing unit is utilised to receive signals from at least two microphones worn on the user's head, which are then processed so as to distinguish as well as possible between sound from the user's mouth and sounds originating from other sources. The distinction is based on the specific characteristics of the sound field produced by own voice, which are due to the fact that the microphones are in the acoustical near-field of the hearing device user's mouth and in the far-field of the other sources of sound, and that arise because the mouth is located symmetrically with respect of the user's head. The combined detector then detects the presence of own-voice when each of the individual characteristics of the signal are in respective ranges. This method too has a relatively high complexity.
Alternatively, a transducer which picks up vibrations within the ear canal caused by vocal activity of the user can be employed.
U.S. Pat. No. 6,041,129 discloses a hearing aid which uses an accelerometer or other rigid body motion sensor attached to the surface of the hearing aid at a point where it most closely comes in contact with the solid portion of the auditory canal. In this way, the accelerometer can sense directly the conductive sound waves created by the user's own voice. Such sound waves can then be either amplified or attenuated, and subsequently mixed with air-borne sound detected by the microphone depending on the user's needs.
US 2007/0009122 A1 discloses a method of own-voice detection achieved by providing a microphone in the auditory channel whose signal level is compared with that of an external microphone.